1. Field of the Invention
The present invention is related to information recording and reproducing apparatus such as a magnetic disk storage apparatus and an optical disk storage apparatus, and particularly to the management of defect sectors occurring in the information storage medium used in such apparatus.
2. Description of Related Art
The recording area of the information storage medium used in a magnetic disk storage apparatus, an optical disk storage apparatus and the like is typically divided into a plurality of concentric annular tracks or a single spiral track, and each track is divided into sectors of a predetermined length. To identify the address of each sector on the information storage medium, an identifier consisting of a sector number, track number, and head number are stored in each sector, enabling the head to read those identifiers to access a desired sector.
FIG. 1(a) is an image of a track for a magnetic disk, and it consists of a user area and an alternate area. Since the magnetic disk storage apparatus with the magnetic disk is not yet shipped, no user data is recorded in the user area. The user area comprises N+1 user sectors of sector numbers 0 to N which are assigned in the order of the physical arrangement of sectors, and each user sector is used for storing user data. The alternate area comprises alternate sectors to be used for storing user data in place of defective user sectors. As to the magnetic disk, in the final inspection of the all sectors in the manufacturing stage, so-called primary defect sectors of low read or write reliability are detected. In FIG. 1(a), the sector number 2 is a primary defect sector detected before the product shipment, and before the user stores programs or data in the disk. Sectors used sequentially according to logical addresses which are assigned skipping the sector number 2. To read the stored data, the head is positioned relative to the disk by a seek or search operation. First, the head is moved in the radial direction of the disk to detect a desired track number, and then the disk rotates and the sectors move relative to the head in the circumferential direction to detect a desired sector number. Since data is stored according to the logical addresses of sectors which are sequentially arranged intra- and inter-tracks, the head can sequentially seek tracks and sequentially search the data as the disk rotates.
FIG. 1(b) represents a state in which, after a magnetic disk storage apparatus is shipped, a defect occurs in a user sector in which user data is stored (hereinafter referred to as a "secondary defect sector," and the user data is stored in an alternate area. In the recording surface of a disk, deterioration is caused by the rewriting of information or the lapse of time, and reliability is reduced in the reading from or the writing to the sectors in which user data is stored. If a read error occurs in which no successful reading can be made in the normal read mode, the magnetic disk storage apparatus performs a rereading in a special read mode in which the read timing is changed or the head position is finely adjusted, and if it determines that the sector reliability has decreased below a predetermined value, it changes the operation of the apparatus so as to use an alternate sector instead of the defective sector. The sector number 5 in FIG. 1(b) is a sector determined to be a secondary defect sector, and the data stored in the sector number 5 is stored in an alternate sector of a sector number N+1. The sector number 5 and the sector number N+1 are associated by a change of the identifier forming each sector or a table provided in the RAM of the controller, and when the logical address 4 of the sector number 5 is addressed, the head is positioned at the sector number N+1 to read the data stored therein. In the reading of the user data stored in the track of FIG. 1(b), the head sequentially performs a search in the order of the physical arrangement of sectors for the logical addresses 0 to 3, and when it reaches the logical address 4, it moves to the sector number N+1 and then returns to the logical address 5.
The alternate area may be provided in the same track, or may be provided in another track. If the alternate sector exists in the same track, the head needs to wait for the disk rotation when it moves from the logical address 3 to the sector number N+1, and if the alternate sector exists in another track, a waiting time is further required for a change of the retrieved track by a seek operation. The mechanical operation needed for such retrieval position change largely reduces the transfer rate of the read/write of the magnetic disk storage apparatus.
Published Unexamined Patent Application No. 6-111479 discloses an invention for improving the transfer rate of an information recording and reproducing apparatus which has been decreased by the occurrence of secondary defect sectors as shown in FIG. 1(b). This method is to rearrange the data in the alternate sectors to the user area by a slipping process and assign logical addresses as shown in FIG. 1(c). That is, logical addresses are assigned skipping the sector number 5 in which a secondary defect has occurred, and the moving of the head to the alternate area is avoided by moving the head according to the assigned logical addresses. Since the logical addresses of the sector number 6 and the succeeding sectors are all assigned after having one subtracted from them, the user data needs to be rewritten so that the memory contents of the sectors according to the original logical addresses match the memory contents of the sectors according to the changed logical addresses, to maintain the logical addresses recognized by the host computer. In accordance with this background art, to prevent the already stored user data from being destroyed when it is rewritten, a memory capable of storing data for at least N+1 sectors is prepared, all the N+1 user data stored in the sectors related to the rewriting are once stored in the memory, logical addresses are assigned by the slipping process as shown in FIG. 1(c), and thereafter the user data stored in the memory are sequentially written according to the logical addresses.
However, in the above background art, to move the user data in alternate sectors to user sectors, a memory is required which has a capacity for storing all the user data needed to be rewritten, and this technique is applicable only to a disk in which the pair of a user area and an alternate area is divided into relatively small units. The reason is that, if the whole user data in the user area corresponding to a certain alternate area is not stored in the memory, data which has not been moved yet will be overwritten. For instance, if the data in the logical address 5 (sector number 6) in FIG. 1(b) is read and written to the logical address 5 (sector number 7) in FIG. 1(c), the data in the sector number 7 is overwritten though it has not been moved yet. On the other hand, to divide the user area into large units is preferable for reducing the number of unused alternate sectors and effectively utilizing the memory space of the disk. Accordingly, this technique cannot be applied to a disk in which one user area and one alternate area are respectively acquired on the whole surface of one disk or over the whole surface of a plurality of disks.
For the rearrangement as shown in FIG. 1(c) of the sectors of a disk in which the user area is divided into units larger than the capacity which can be stored in the memory, conventionally the user data was sequentially rewritten in increasing order of sector number. At this point, the user data after the secondary defect sector (in this case, the sector number 5) are all overwritten with the data stored in other logical address, and thus the original user data could not be maintained after the rearrangement. Further, if the user data needs to be maintained, all the data were once transferred to another storage device for evacuation, and were written after the logical addresses of the disk were newly assigned.